Transmitter with anode voltage modulation



Feb; 17, 19

M. FAVRE Filed Feb. 16, 1945 2 Sheets-Sheet l Feb. 17, 1948. M. FAVRE TRANSMITTER WITH ANODE VOLTAGE MODULATION 2 sheets-sheet 2 Filed Feb. l6, I945 Patented Feb. 17, 1948 -TRAN SMITTER-WITH 'ANDDEVOLTAGE MODULATION Marcel Fayre, 'Wettingen, Switzerland, assignor to fl atelh'old Patentverwertungs-lfi Elektro- Holding A.-"G., Glarus, Switzerland Application-February 16, 1945, Serial-'No.*'.5 78,207 In Switzerland January 4, 1944 Section 1, Public Law 690, August s, 1946 Patent-expires January 4, 19.64

11 Claims.

The present invention concerns an arrangement for modulating the anode voltage ofthe high frequency power stage of a transmitter consisting of a high and low frequency part. With such an 'arrangement'analteration in the anode voltage alsocauses the interval of time dur- "sing'which the anode current flows or the anode current flow angle to vary. With modulation peaks of the low frequency modulation voltages this angle becomes larger, the efficiency correspcndingly lower and the maximum power output too small. The modulation characteristic II shown in Fig. 1 which" represents the relationship between the high frequency anode alternating voltage Ew and the anode direct voltage Ea for-a constant alternating grid voltage, is thus a curve and not the desired straight line I. Due to the non-linear connection between the values Ew and En appreciabledistortions are caused with a high degree'of modulation. In addition there are also distortions due to a variation in. the load resistance of the modulator'which is formed bythe high frequency power stage.

These disadvantages are avoidedaccording to the invention by the control grid bias voltage of the high frequency power stage and simultaneously theanode voltage of the tube stage in front of the high frequency power stage being subjected in'opposite phase and in phase respectively toa modulation with a modulation depth at least about equal to the anode voltage of the high frequency power stage.

The invention possesses several advantages when compared with known arrangements. Since the power of the stage in front of the h gh frequency power stage is regulated by altering the anode voltage in rhythm with the modulation voltage. this is only subjected to a maximum'l'oad during the voltage peaks and not continuously. The mean power required can thus be considerably reduced for this stage so that the life of the tubes in this stage-are considerably prolonged. The. average efficiency of. the end stage becomes greater, because it does not decrease during the-voltage peaks but maintains its value; at the same time the distortions become smaller. Furthermore the improved effici'ency enables the tubesto be better utilized. Finally it is possible by means of suitable small deviations of the modulation depth of thecontrol grid bias voltage of the high frequency power stage and or the anode voltage. of the tube stagein front of this curve-which is identic l with that of the modulation depth of'the anodevoltage of the high ire. quencypowerst'age, thus eliminating distori'li'im -s.

In the drawings which illustrategconstruc tional examples' ofthe invention, Fig. 1, already referred to, is a plot showing the relationship between'anodedirect voltage and high frequency:

alternating voltage with constant alternating grid voltage; Fig. '2 is a schematic diagram of oneiorm of 'the inven'tion; Fig. 3 is a plot showing the grid voltage-anode current characteristic of a tube; and Fig. 4 is a schematic view of a modified "fforr'n of the invention. The high frequency carrier oscillations are produced in the high frequency 'part of the transmitter are; rangement shownin theupper portion of Figures 2*"an'd 4. "The low frequency amplifier shown below serves 130"?0111'1 *the modulation voltages. In Fig. '2 reference numeral l indicatesan oscillator-Tor producing high frequency "(Ri a oscillations which reach the 7 grid of-tube '2 where they are amplified. In the anode circuit ofthis tube is a-n oseiIl-ationcireuit 3 which actsas a load. "If necessary a frequency multiplication can be combined with this amplification.

The high frequency alternating voltages are taken from this oscillation circuit 3 and passed over acoupllng condenser to the grid'of the next stage. The grid circuit of this "stage formed by an inductance 4, agrid bias voltage source fi and-achoke coil 6 which doesnotallow low:frequenciestopass, these elements being connected in series. Tube 1 is-c-onnected to an oscillation circ'uitt from whence the poweris supplied toan antenna or a further stage.

The speech frequencies'are amplified in a low frequency -'a1np1ifier. This consists of the audio or' sp'eech frequency (AF) source H, tubes 12' operating in ipush+pull connection, and transformer l3. lnparallel with the secondary win'ding ofthe' 'latter-isa choke-coil l4. Theanode voitag'e'passestb terminal l 5. Condenser 16' pre vents the direct-anode current oftube 'l from flowing through the "secondarywinding of transformer-f3. .Th'is currentfinds a path through choke coil 16.

In service a voltage drop; which also appears at choke'coil i4;-'occur's in the secondary winding of-transformerl3in rhythm with the speechfrequenciessuppliedto' the-amplifier I i. ,"By this means oscillations areobtained in oscillation circuit t the amplitude of which'varies in rhythm with the low frequency signahand thus thehigh. frequency oscillatim'is' amplified in tube 1 have their amplitude modulated.

If now: iat ai certain" moment due to the lowfrequency amplification, the voltage drop at choke coil l4 becomes smaller and thus the anode voltage of tube 1 greater, the grid voltage and anode current characteristic III in Fig. 3 will be displaced to the left in the direction of the negative grid voltage. This figure shows in a known manner the course of the anode current in as a function of the grid voltage e a sinusoidal alter- 4 An important feature of these arrangements is that it is immaterial if the magnitude of the voltage variations is not exactly proportional with the modulation depth of the alternating anode voltage of tube I. Since namely by means of small deviations of the voltage variations from such a proportional curve it is possible to ensure nating voltage being shown in the lower part of the figure as a function of the time T. From Fig. 3 it is clear that when the curve III is moved to the left, the grid bias voltage remaining unchanged, the time interval during which the anode current flows (indicated by the angle becomes greater, whilst the time interval during;

which no anode current flows becomes smaller due to the anode voltage increasing. This is known to decrease the efiiciency. This disadvantage can now be avoided, if for instance when doubling the anode voltage of the tube 1 its grid bias voltage is also doubled in a negative sense,

whilst at the same time the anode voltage of in Fig. 2 the voltage for modulating the anode voltage of tube 2 is obtained at point I! of choke coil l4 and supplied over oscillation circuit 3 to the anode of this tube. By this means it is possible to maintain the current flow angle 0 and therefore the efiiciency of tube 1 constant.

By tapping the voltage off at the point I! the depth of the modulation can be correctly ad-' justed if the anode voltage of tube 2 differs from that of tube '1. Even if the anode voltage are equal choke coil [4 provides a useful means of adjustment.

Amodified form of the invention is illustrated in Fig. 4. Elements corresponding to those already shown in Fig. 2 are indicated by the same reference numerals, so that these elements and their method of operation do not require to be described again. In the modified arrangement shown in Fig. 4 the modulated high frequency stage, which can be an end or intermediate stage, consists of two tubes I inpush-pull connection. Transformer 2| serves to control the grid and anode voltages. The primarywinding 22 of the transformer has an alternating anode current flowing through itbecause that half of the choke coil 9 which is at the cathode side prevents this current. from flowing to earth. This alternating anode voltage produces two voltages in transformer 2!, one of which lies across the winding 23; it serves to influence the grid bias voltage The second voltage which is necof tubes 1. essary for controlling the anode voltage of tube [is taken from the secondary winding 24. It is fed over condenser 25, which is required to sep arate the "direct anode-voltage from the earth.

advantage of the arrangement .shown inv Fig. 4 is that the power required for the additionalanode and grid modulation is obtained from the cathode circuit of the high frequency and stage. This power extraction has the character of a feed-back coupling and possesses the advantages inherent to such a connection.

that the modulation characteristic II in Fig. 1 assumes a straight line course corresponding to the characteristic I, a particular advantage of the arrangement according to Fig. 2 or 4 is that the anode voltage modulation is free from distortion and the efliciency also remains constant.

The arrangement in Fig. 2 can be simplified if choke'coil I4 is omitted. In this case the anode current of tubes 2 and I flows through the secondary side of transformer l3.

In order to be able to obtain the correct phase position for the feed back voltages, it is advisable to conduct these voltages over phase-adjusting elements.

The high power stage formed by tubes 1 can consist of a single tube or several tubes connectedin push-pull or in parallel. It is preferably connected in such a manner that it oper-' ates as a class C amplifier. The tubes of this stage can also be operated in class B or A, with-'j' out the advantages resulting from the invention being thereby affected.

I claim:

1. In a transmitter, a high frequency part comprising; an oscillator producing a high frequency carrier wave, an amplifier stage arranged for amplifying the output of said oscillator, and a power stage connected to the output of aid amplifier stage; a low frequency part comprising a source of audio frequency modulating potential; means to modulate the amplitude of said carrier wave in accordance with said modulating potential; and means simultaneously subjecting the grid bias potential of said power stage and the anode potential of said amplifier stage in opposite phase and in phase, respectively, to a modulation having a modulation depth at least approximately etqual to that of the anode potential of said power s age.

2. A transmitter as defined in claim 1, characterized by the feature that said last means includes a transformer, one winding of which has at least a part of the alternating anode current of said power stage flowing through it. i

3. A transmitter as defined in'claim 1, char acterized by the feature that said source of audio frequency modulating potential includes a power amplifier'stage and that last said means includes at least one choke coil connected in circuit with' said audio frequency power amplifier stage from which is taken at least part of the alternating anode potential ofsaid high frequency amplifier, stage to modulate the anode potential thereof.

4. A transmitter as defined in claim 1, char,- acterized by the feature that the anode voltages: of the amplifier and power stages respectively of said high frequencypart are equal.

i 5. A transmitter as defined in claim 1, charaoterized by the feature that said last means m cludes a transformer connected in the anode cir-P cult; of the power stage of said high frequency, par 6. A transmitter as defined in claim 1, charac' terized by the feature that said last means ineludes a transformer connected in the cathode circuit of the power stage of said high frequency part.

7.. A transmitter as defined inclaim 1,- charac acting on the primary winding of said trans former, the alternating anode current of the power stage of said high frequency part flowing between an end point in the secondary winding. of said transformer, said end point being located between said winding point and the anode of said high frequency power stage, the potential at the other end point of said secondary winding being supplied to the grid of said high frequency power stage.

8. A transmitter as defined in claim 1, char; l5 acterized by the feature that said last means includes a transformer connected in the anode cir-f cult of the power stage of said high frequency part, the end stage of the low frequency part acting on the primary winding of said trans former, the alternating anode current of the power stage of said high frequency part flowing between an end point in the secondary winding of said transformer, said end point being located between said winding point and the anode of said high frequency power stage, the potential at the other end point of said secondary winding being; supplied to the grid of said high frequency power stage, and a choke coil connected in parallel to that part of the transformer secondary winding fso through which the alternating anode current of the high frequency power stage flows, said choke coil supplying the potential required for modulating the anode potential of said high frequency amplifier stage.

9. A transmitter as defined in claim 1, characterized by the feature that said last means in- 2,4saoec 6 cludes a transformer connected in the cathode circuit of the power stage of said high frequency part, at least part of the primary winding of said transformer having alternating anode current of the high frequency power stagv'flowing through it, and the potential for modulating the .anode potential of the high frequencyiamplifier stage is taken from the secondary of said transformer.

10. A transmitter as defined in claim 1, characterized by the feature that saidlast means includes a transformer connected in the cathode circuit of the power stage of said high frequency part, a part of the primary winding of said transformer having alternating anode current of the high frequency power stage flowing through it, and the potential across the remaining part of the primary winding being supplied to the control grid of the high frequency power stage.

11. A transmitter as defined in claim 1, and further including phase adjusting means for ad-- justing the phase of at least one of the modulating potentials to which said grid and anode are simultaneously subjected.

MARCEL FAVRE.

REFERENCES CITED The following references are of record in the file of this patent: I

UNITED STATES PATENTS Number Name Date 2,138,653 Dome Nov. 29, 1938 2,226,258 Reise et al Dec. 24, 1940 FOREIGN PATENTS Number Country Date 118,096 Australia Mar. 26, 1942 

